diff --git a/compiler/test/dotty/tools/vulpix/RunnerOrchestration.scala b/compiler/test/dotty/tools/vulpix/RunnerOrchestration.scala
index bec8b83b4497..779df71b7ba6 100644
--- a/compiler/test/dotty/tools/vulpix/RunnerOrchestration.scala
+++ b/compiler/test/dotty/tools/vulpix/RunnerOrchestration.scala
@@ -159,7 +159,7 @@ trait RunnerOrchestration {
       val url = classOf[ChildJVMMain].getProtectionDomain.getCodeSource.getLocation
       val cp = Paths.get(url.toURI).toString + JFile.pathSeparator + Properties.scalaLibrary
       val javaBin = Paths.get(sys.props("java.home"), "bin", "java").toString
-      new ProcessBuilder(javaBin, "-Dfile.encoding=UTF-8", "-Xmx1g", "-cp", cp, "dotty.tools.vulpix.ChildJVMMain")
+      new ProcessBuilder(javaBin, "-Dfile.encoding=UTF-8", "-Duser.language=en", "-Duser.country=US", "-Xmx1g", "-cp", cp, "dotty.tools.vulpix.ChildJVMMain")
         .redirectErrorStream(true)
         .redirectInput(ProcessBuilder.Redirect.PIPE)
         .redirectOutput(ProcessBuilder.Redirect.PIPE)